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From: Juan Christian <juan0christian@gmail.com>
Date: Thu, 18 Dec 2014 01:04:18 +0000
Subject: Re: Is there a way to schedule my script?
To: "Steven D'Aprano" <steve+comp.lang.python@pearwood.info>, python-list@python.org
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On Wed Dec 17 2014 at 9:40:52 PM Steven D'Aprano <
steve+comp.lang.python@pearwood.info> wrote:

> Juan Christian wrote:
>
> > I know about the schedule modules and such but they work in situations
> > like 'run this in a X hours/minutes/seconds interval', I already have my
> > code in a while loop with sleep (it's a bit ugly, I'l change to a
> > scheduler soon).
> [...]
> > I want my script to start at a given time and stop at another given time,
> > is that possible?
>
> The right solution to this is probably to use your operating system's
> scheduler to run your script at whatever time or times you want. Under
> Unix/Linux, that is cron. I'm sure Windows will have it's own, but I don't
> know what it is.
>
> Then your script then doesn't have to care about times at all, it just runs
> and does its thing, and the OS controls when it runs. cron is amazingly
> flexible.
>
> This is the proper separation of concerns. Your script doesn't have to deal
> with memory management, or the file system, or scheduling times, that is
> the operating system's job. The OS already has tools to do this, and can do
> them *much better than you*. (What happens if your script dies? What about
> when the time changes, say because of daylight savings?)
>
> Unless you are running on some primitive OS with no way to control when
> jobs
> run except to manually run them, the *wrong* solution is a busy-wait loop:
>
> while True:
>     # Wait forever, doing nothing.
>     sleep(0.1)  # Yawn.
>     if now() == some_time():
>         do_this()
>
>
> It doesn't matter if you use the sched module to shift the time check to
> another part of your code if the main loop does nothing. The critical
> question here is this:
>
> While you are waiting for the scheduled time, does your main loop
> continuously do any other work?
>
> If the answer is Yes, then using sched is the right approach.
>
> If the answer is No, then your main loop is just killing time, doing
> nothing
> but sleeping and waiting, like somebody checking their wristwatch every two
> seconds. You should simplify your script by getting rid of the main loop
> completely and let your OS handle the timing:
>
> # No loop at all.
> do_this()
>

Thanks. That was a great answer. I'll redo my code. It's running and will
only run in my Docker container (Ubuntu Server 14.04.1) so I'll use cron.

Indeed, currently I'm using something like that:

while True:
    if 9 < datetime.now().hour < 24:
        # do stuff
        sleep(randint(3, 6) * 60)
    else:
        # see you in 9 hours
        sleep(9 * 60 * 60)

I knew it wasn't a good approach, but as least it was running as intended!

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<br><br><div class=3D"gmail_quote">On Wed Dec 17 2014 at 9:40:52 PM Steven =
D&#39;Aprano &lt;<a href=3D"mailto:steve%2Bcomp.lang.python@pearwood.info">=
steve+comp.lang.python@pearwood.info</a>&gt; wrote:<br><blockquote class=3D=
"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding=
-left:1ex">Juan Christian wrote:<br>
<br>
&gt; I know about the schedule modules and such but they work in situations=
<br>
&gt; like &#39;run this in a X hours/minutes/seconds interval&#39;, I alrea=
dy have my<br>
&gt; code in a while loop with sleep (it&#39;s a bit ugly, I&#39;l change t=
o a<br>
&gt; scheduler soon).<br>
[...]<br>
&gt; I want my script to start at a given time and stop at another given ti=
me,<br>
&gt; is that possible?<br>
<br>
The right solution to this is probably to use your operating system&#39;s<b=
r>
scheduler to run your script at whatever time or times you want. Under<br>
Unix/Linux, that is cron. I&#39;m sure Windows will have it&#39;s own, but =
I don&#39;t<br>
know what it is.<br>
<br>
Then your script then doesn&#39;t have to care about times at all, it just =
runs<br>
and does its thing, and the OS controls when it runs. cron is amazingly<br>
flexible.<br>
<br>
This is the proper separation of concerns. Your script doesn&#39;t have to =
deal<br>
with memory management, or the file system, or scheduling times, that is<br=
>
the operating system&#39;s job. The OS already has tools to do this, and ca=
n do<br>
them *much better than you*. (What happens if your script dies? What about<=
br>
when the time changes, say because of daylight savings?)<br>
<br>
Unless you are running on some primitive OS with no way to control when job=
s<br>
run except to manually run them, the *wrong* solution is a busy-wait loop:<=
br>
<br>
while True:<br>
=C2=A0 =C2=A0 # Wait forever, doing nothing.<br>
=C2=A0 =C2=A0 sleep(0.1)=C2=A0 # Yawn.<br>
=C2=A0 =C2=A0 if now() =3D=3D some_time():<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 do_this()<br>
<br>
<br>
It doesn&#39;t matter if you use the sched module to shift the time check t=
o<br>
another part of your code if the main loop does nothing. The critical<br>
question here is this:<br>
<br>
While you are waiting for the scheduled time, does your main loop<br>
continuously do any other work?<br>
<br>
If the answer is Yes, then using sched is the right approach.<br>
<br>
If the answer is No, then your main loop is just killing time, doing nothin=
g<br>
but sleeping and waiting, like somebody checking their wristwatch every two=
<br>
seconds. You should simplify your script by getting rid of the main loop<br=
>
completely and let your OS handle the timing:<br>
<br>
# No loop at all.<br>
do_this()<br></blockquote><div><br></div><div>Thanks. That was a great answ=
er. I&#39;ll redo my code. It&#39;s running and will only run in my Docker =
container (Ubuntu Server 14.04.1) so I&#39;ll use cron.</div><div><br></div=
><div>Indeed, currently I&#39;m using something like that:</div><div><br></=
div><div>while True:</div><div>=C2=A0 =C2=A0 if=C2=A09 &lt; datetime.now().=
hour &lt; 24:</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 # do stuff</div><div>=
=C2=A0 =C2=A0 =C2=A0 =C2=A0=C2=A0sleep(randint(3, 6) * 60)</div><div>=C2=A0=
 =C2=A0 else:</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 # see you in 9 hours</d=
iv><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0=C2=A0sleep(9 * 60 * 60)</div><div><br><=
/div><div>I knew it wasn&#39;t a good approach, but as least it was running=
 as intended!</div></div>

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